Radio station, radio terminal, and method for terminal measurement

ABSTRACT

A radio station (1) transmits, to a radio terminal (3) on a licensed frequency (Cell #1), control signaling (S102) associated with at least one of a measurement timing and a measurement period of terminal measurement on an unlicensed frequency (Cell #2) and receives, from the radio terminal (3) on the licensed frequency (Cell #1), a result of the terminal measurement that is executed in response to the control signaling (S102) and in accordance with at least one of the measurement timing and the measurement period (S105). This contributes, for example, to acquisition of information useful for the radio station to determine whether to allow the radio terminal to perform communication on the unlicensed frequency.

TECHNICAL FIELD

The present application relates to a radio communication system in whicha radio station performs communication with a radio terminal on anunlicensed frequency or a shared frequency.

BACKGROUND ART

In order to improve the degradation of communication quality due to asharp recent increase in mobile traffic and to provide faster 15high-speed communication, the 3GPP Long Term Evolution (LTE) hasspecified the Carrier Aggregation (CA) function that enables a radioterminal (User Equipment (UE)) to communicate with a radio base station(eNode B (eNB)) by using a plurality of cells. Note that cells that a UEcan use in CA are limited to a plurality of cells of a single eNB (i.e.,a plurality of cells operated or managed by a single eNB). The cellsused by the UE in CA are categorized into a primary cell (PCell) thathas already been used as a serving cell when CA is started and asecondary cell(s) (SCell(s)) that is used additionally or in a dependentmanner. In the PCell, when a radio connection is (re-)established (RadioResource Control (RRC) Connection Establishment, RRC ConnectionRe-establishment), Non Access Stratum (NAS) mobility information andsecurity information (security input) are transmitted (see section 7.5of Non-Patent Literature 1).

From a functional point of view, the introduction of CA has enabledhigh-speed communication. In practical usage, however, it is consideredthat it would be difficult to address the issue of a further increase inmobile traffic in the future due to limitations (shortage) offrequencies allocated to each operator. Accordingly, in the 3GPPstandardization process, discussions on Unlicensed LTE that executes LTEwith the use of an unlicensed frequency (unlicensed frequency band,unlicensed spectrum) have been started (Non-Patent Literature 2 and 3).Unlicensed LTE is also referred to as LTE-U or U-LTE and is hereinafterreferred to as LTE-U.

As methods for achieving LTE-U, two methods, i.e., Licensed AssistedAccess (LAA) in which the eNB performs communication with the UE on theunlicensed frequency in association with the licensed frequency (e.g.,as SCell of CA) and Standalone (SA) in which the eNB performscommunication with the UE only on the unlicensed frequency, areconsidered. The unlicensed frequency is, for example, 5 GHz band, whichis also used by other systems such as radar systems and wireless LAN(WLAN or also referred to as WiFi). Therefore, with regard to the SAscheme in which communication is performed only on the unlicensedfrequency, it would be difficult to implement sophisticated controlsspecified for LTE and thus the more feasible LAA scheme (also referredto as LA-LTE) has mainly been discussed. In the following description,LTE-U by the LAA scheme, in which CA using the licensed frequency andthe unlicensed frequency is performed, will be mainly explained. Thelicensed frequency means a dedicated frequency allocated to a specificoperator. The unlicensed frequency means a frequency that is notallocated to a specific operator or a shared frequency allocated to aplurality of operators. In the latter case, this frequency may bereferred to as a licensed shared frequency, not an unlicensed frequency,and communication using this frequency is also referred to as a LicensedShared Access (LSA). In the following description, frequencies otherthan licensed frequencies licensed only to any specific operators arecollectively referred to as an unlicensed frequency.

LTE-U by the LAA scheme is basically executed in accordance with thesequence shown in FIG. 15. In this example, it is assumed that the eNBperforms data transmission (or reception) with a UE #1 in a Cell #1,which is the licensed frequency, and a cell #2, which is the unlicensedfrequency. First, a radio connection is established between the eNB andthe UE #1 in the Cell #1 (RRC Connection Establishment, S901) and abearer is established between a core network (Evolved Packet Core: EPC)and the UE #1 (not shown). That is, the Cell #1 becomes the PCell forthe UE #1. When there is downlink (DL) user data (also referred to asUser Plane (UP) data) to be transmitted to the UE #1 or when there isuplink (UL) user data that the UE #1 wants to transmit, the eNBtransmits or receives this user data in the Cell #1 (DL (or UL) UP datatransmission, S902).

Next, when the eNB determines that it is efficient for the UE #1 totransmit and receive user data in the Cell #2 at some point (TriggerLTE-U for UE #1, S903), the eNB transmits, to the UE #1 in the Cell #1,control information about radio resource configuration for the Cell #2(Radio Resource Configuration for Cell #2, S904). This controlinformation corresponds to a RadioResourceConfigDedicated InformationElement (IE) and a RadioResourceConfigCommon IE transmitted in an RRCConnection Reconfiguration message of the LTE (Non-Patent Literature 4).The Cell #2 hereby becomes the SCell for the UE #1. When the user datais transmitted in the downlink, the eNB performs sensing in the Cell #2to determine whether the Cell #2 is available (Perform channel sensing.S905). Upon determining that the Cell #2 is available, the eNB transmitsor receives user data to or from the UE #1 (DL (or UL) UP datatransmission, S906). As described above, by the use of the unlicensedfrequency, it is expected that the throughput will be further improvedor the cell capacity will be increased.

The aforementioned sensing is referred to as Listen Before Talk (LBT)(Non-Patent Literature 2), which determines whether LTE-U by anotheroperator or communication of another radio system (e.g., WLAN) isperformed nearby on the target unlicensed frequency. The aforementionedsensing corresponds to, for example, Channel Availability Check (CAC)for radar systems and Clear Channel Assessment (CCA) executed by a WLANAccess Point (AP) (Patent Literature 1).

CITATION LIST Non-Patent Literature

-   [Non-Patent Literature 1] 3GPP TS 36.300 V12.2.0 (2014-06), “3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA)    and Evolved Universal Terrestrial Radio Access Network (E-UTRAN);    Overall description; Stage 2 (Release 12)”, June, 2014-   [Non-Patent Literature 2] 3GPP RP-131635, “Introducing LTE in    Unlicensed Spectrum”, Qualcomm, Ericsson, December, 2013-   [Non-Patent Literature 3] 3GPP workshop on LTE in unlicensed    spectrum, RWS-140002, “LTE in Unlicensed Spectrum: European    Regulation and Co-existence Considerations”, Nokia, June, 2014-   [Non-Patent Literature 4] 3GPP TS 36.331 V12.2.0 (2014-06), “3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA);    Radio Resource Control (RRC); Protocol specification (Release 12)”,    June, 2014-   [Non-Patent Literature 5] 3GPP TR 36.842 V12.0.0 (2013-12), “3rd    Generation Partnership Project; Technical Specification Group Radio    Access Network; Study on Small Cell enhancements for E-UTRA and    E-UTRAN; Higher layer aspects (Release 12)”, December, 2013

Patent Literature

[Patent Literature 1] U.S. Pat. No. 7,443,821

SUMMARY OF INVENTION Technical Problem

In the aforementioned background art, it is assumed that the basestation (eNB) determines whether to allow the UE to performcommunication in the cell (the Cell #2) on the unlicensed frequencybased on terminal measurement report by the UE (measurement report byUE). For example, the eNB transmits to the UE in the cell on thelicensed frequency (the Cell #1) an instruction for sending terminalmeasurement report, and the UE executes terminal measurement in the cellon the unlicensed frequency (the Cell #2 or the like) and reports,through the Cell #1, the result of the terminal measurement. The eNBdetermines whether it is appropriate to transmit user data to the UE inthe Cell #2 based on the result of the terminal measurement in the Cell#2. The eNB may determine, for example, whether the reception quality(RSRP or RSRQ) of a reference signal (RS) in the cell (the Cell #2 orthe like) on the unlicensed frequency is equal to or larger than apredetermined value. When the eNB determines that the Cell #2 isappropriate for user data transmission, the eNB transmits user data tothe UE (e.g., the UE #1 in Background Art) in the Cell #2.

However, if the terminal measurement report of normal LTE is used, thereis a possibility that an appropriate UE is sometimes not allowed toperform communication (in a cell) on the unlicensed frequency. This isbecause, since the unlicensed frequency is shared with othercommunication systems as described above, the reference signal is notalways transmitted, unlike in a cell of LTE. For example, the UE mightcalculate a value for the terminal measurement report by averagingreception quality during the period in which a reference signal istransmitted from another radio system and reception quality during theperiod in which the reference signal is not transmitted (in this case,the resulting value becomes an invalid value). Then the receptionquality on the unlicensed frequency indicated in the terminalmeasurement report might be calculated to be lower than a thresholdlevel that is defined to determine that it is appropriate to performcommunication (in a cell) on the unlicensed frequency. In this case,even when it is determined that the unlicensed frequency is availablebased on the aforementioned sensing by the eNB (S905 in FIG. 15), unlessan appropriate UE is allowed to use the unlicensed frequency, it may beimpossible to provide sufficient improvement of performance (e.g.,improvement of the throughput or increase in the cell capacity) by theuse of the unlicensed frequency.

Accordingly, an object to be attained by embodiments disclosed herein isto provide an apparatus, a method, and a program that contribute toacquisition of information useful for a radio station (e.g., an eNB) toaccurately determine whether to allow a radio terminal (e.g., a UE) toperform communication (in a cell) on an unlicensed frequency.

Solution to Problem

In a first aspect, a method performed in a radio station includes: (a)communicating with a radio terminal on a licensed frequency; (b)transmitting, to the radio terminal on the licensed frequency, controlsignaling associated with at least one of a measurement timing and ameasurement period of terminal measurement on an unlicensed frequency:and (c) receiving, from the radio terminal on the licensed frequency, aresult of the terminal measurement executed in accordance with at leastone of the measurement timing and the measurement period in response tothe control signaling.

In a second aspect, a radio station includes a radio communication unit(a transceiver) and a control unit (a controller). The radiocommunication unit is configured to communicate on a licensed frequencyand an unlicensed frequency. The control unit is configured to:transmit, to the radio terminal on the licensed frequency, controlsignaling associated with at least one of a measurement timing and ameasurement period of terminal measurement on the unlicensed frequency:and receive, from the radio terminal on the licensed frequency, a resultof the terminal measurement executed in accordance with at least one ofthe measurement timing and the measurement period in response to thecontrol signaling.

In a third aspect, a method performed in a radio terminal includes: (a)communicating with a radio station on a licensed frequency; (b)receiving, from the radio station on the licensed frequency, controlsignaling associated with at least one of a measurement timing and ameasurement period of terminal measurement on an unlicensed frequency;(c) executing the terminal measurement in accordance with at least oneof the measurement timing and the measurement period in response to thecontrol signaling, and (d) transmitting a result of the terminalmeasurement to the radio station on the licensed frequency.

In a fourth aspect, a radio terminal includes a radio communication unit(a transceiver) and a control unit (a controller). The radiocommunication unit is configured to communicate with a radio station ona licensed frequency and an unlicensed frequency. The control unit isconfigured to: receive, from the radio station on the licensedfrequency, control signaling associated with at least one of ameasurement timing and a measurement period of terminal measurement onthe unlicensed frequency; execute the terminal measurement in accordancewith at least one of the measurement timing and the measurement periodin response to the control signaling; and transmit a result of theterminal measurement to the radio station on the licensed frequency.

In a fifth aspect, a program includes instructions (software codes)that, when loaded into a computer, causes the computer to perform themethod according to the aforementioned first aspect.

In a sixth aspect, a program includes instructions (software codes)that, when loaded into a computer, causes the computer to perform themethod according to the aforementioned third aspect.

In a seventh aspect, a method for terminal measurement includes: (a)transmitting, from a radio station to a radio terminal on a licensedfrequency, control signaling associated with at least one of ameasurement timing and a measurement period of terminal measurement onan unlicensed frequency; (b) executing the terminal measurement by theradio terminal in accordance with at least one of the measurement timingand the measurement period in response to the control signaling; and (c)transmitting a result of the terminal measurement from the radioterminal to the radio station on the licensed frequency.

Advantageous Effects of Invention

According to the aforementioned aspects, it is possible to provide anapparatus, a method, and a program that contribute to acquisition ofinformation useful for a radio station (e.g., an eNB) to determinewhether to allow a radio terminal (e.g., a UE) to perform communication(in a cell) on the unlicensed frequency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a diagram showing a configuration example of a radiocommunication system and another radio system according to severalembodiments:

FIG. 1B is a diagram showing a configuration example of the radiocommunication system and the other radio system according to severalembodiments;

FIG. 2 is a diagram showing a configuration example of the radiocommunication system and the other radio system according to severalembodiments;

FIG. 3 is a sequence diagram showing one example of operations of aradio base station and a radio terminal according to a first embodiment;

FIG. 4 is a sequence diagram showing one example of operations of theradio base station and the radio terminal according to the firstembodiment (specific example 1);

FIG. 5 is a diagram showing one example of terminal measurement by theradio terminal according to the first embodiment (specific example 2);

FIG. 6 is a diagram showing one example of terminal measurement by theradio terminal according to the first embodiment (specific example 3);

FIG. 7 is a diagram showing one example of terminal measurement by theradio terminal according to the first embodiment (specific example 4);

FIG. 8 is a sequence diagram showing one example of operations of aradio base station and a radio terminal according to a secondembodiment;

FIG. 9 is a diagram showing a configuration example of the radiocommunication system and the other radio system according to severalembodiments;

FIG. 10 is a sequence diagram showing one example of operations of tworadio base stations and a radio terminal according to a thirdembodiment:

FIG. 11 is a sequence diagram showing an example of operations of tworadio base stations (an MeNB and an SeNB) according to the thirdembodiment (specific example 5);

FIG. 12 is a sequence diagram showing an example of operations of thetwo radio base stations (the MeNB and the SeNB) according to the thirdembodiment (specific example 6);

FIG. 13 is a block diagram showing a configuration example of a radiobase station according to several embodiments;

FIG. 14 is a block diagram showing a configuration example of a radioterminal according to several embodiments; and

FIG. 15 is a sequence diagram showing one example of operations of aradio base station and a radio terminal in LTE-U.

DESCRIPTION OF EMBODIMENTS

Specific embodiments are explained hereinafter in detail with referenceto the drawings. In the drawings, the same or corresponding elements aredenoted by the same reference signs, and repetitive descriptions will beavoided as necessary for clarity of explanation.

Embodiments described below will be explained mainly using specificexamples with regard to an Evolved Packet System (EPS) that contains LTEand System Architecture Evolution (SAE). However, these embodiments arenot limited to being applied to the EPS and may also be applied to othermobile communication networks or systems such as a 3GPP Universal MobileTelecommunications System (UMTS), a 3GPP2 CDMA2000 system (1×RTT, HRPD(High Rate Packet Data)), a global system for mobile communications (GSM(registered trademark))/General packet radio service (GPRS) system, anda WiMAX system.

First Embodiment

First, some examples of Unlicensed LTE using an unlicensed frequency(Unlicensed frequency band, Unlicensed spectrum) according to aplurality of embodiments including this embodiment will be described.The Unlicensed LTE is also referred to as LTE-U or U-LTE and ishereinafter referred to as LTE-U. The unlicensed frequency includes afrequency that is used for, for example, radar systems and wireless LAN(WLAN or also referred to as WiFi) and includes frequencies other thanlicensed frequencies allocated only to any specific operators (i.e.,service providers). The unlicensed frequency is, for example, but notlimited to, 5 GHz band. Further, the plurality of embodiments describedbelow can also be applied to a shared frequency (Shared frequency band,Shared spectrum) commonly allocated to a plurality of operators. In thefollowing description, frequencies other than licensed frequencies arecollectively referred to as the unlicensed frequency.

FIGS. 1A, 1B, and 2 are diagrams each showing a configuration example ofa radio communication system of LTE-U and another system according tothe plurality of embodiments including this embodiment. In the exampleshown in FIG. 1A, the radio communication system includes a radio basestation of LTE (eNB) 11 and a radio terminal (UE) 3. The eNB 11 and theUE 3 are configured to perform communication according to normal LTE ona licensed frequency (F1) and to perform communication according toLTE-U on an unlicensed frequency (F2). On the other hand, the unlicensedfrequency (F2) is used for communication between a wireless LAN accesspoint (WLAN AP) 4 and a wireless LAN terminal (WLAN Terminal) 5 as well.Besides the example shown in FIG. 1A, in the example shown in FIG. 1B,the LTE eNB 11 manages a remote base station 12 (RRH or RRE) and usesthe remote base station 12 to perform communication according to LTE-Uon the unlicensed frequency (F2).

The configuration shown in FIG. 1A and that shown in FIG. 1B may coexistin the same system. Further, FIGS. 1A and 1B show only a part of theradio communication system that is considered in this example. Inreality, there are a plurality of eNBs and their RRHs/RREs and aplurality of UEs around the eNB 11, the RRH/RRE 12, and the UE 3, and aplurality of cells on the licensed frequency are managed by these eNBsand RRHs/RREs. Further, there may be a plurality of WLAN APs and aplurality of WLAN Terminals around the eNB 11, the RRH/RRE 12, and theUE 3. In the following description, the term “radio base station 1” or“LTE-U eNB 1” is used to indicate any eNB having the function of LTE-U.That is, the radio base station 1 or the LTE-U eNB 1 corresponds to theeNB 11 in the configuration shown in FIG. 1A and corresponds to the eNB11 and the RRH/RRE 12 in the configuration shown in FIG. 1B. For thesake of convenience of explanation, only a node corresponding to theRRH/RRE 12 n the configuration shown in FIG. 1B may be referred to asthe radio base station 1 or the LTE-U eNB 1.

FIG. 2 is a configuration example of the radio communication system ofLTE-U and another radio communication system when the unlicensedfrequency is particularly noted. There are a radio base station (LTE-UeNB-A) 1A having the function of LTE-U of one operator (serviceprovider) A and a radio terminal (UE for Operator A: UE-A) 3A capable ofbeing connected to a network of the operator A. There also are a radiobase station (LTE-U eNB-B) 1B having the function of LTE-U of anotheroperator (service provider) B and a radio terminal (UE for Operator B:UE-B) 3A capable of being connected to a network of the operator B. Eachof the LTE-U eNBs 1A and 1B corresponds to, for example, the eNB 11 andthe RRH/RRE 12 in FIGS. 1A and 1B and is also referred to as an LTE-UAP, which means an access point of LTE-U. Further, similar to FIGS. 1Aand 1B, there are WLAN APs 4 and WLAN Terminals 5 around the LTE-U eNBs1A and 1B and the UEs 3A and 3B.

In the aforementioned description and the following description, it isassumed that LTE-U is implemented using LAA (also referred to asLA-LTE). As already stated above, in LAA, the radio base station (LTE-UeNB) 1 and the radio terminal (UE) 3 perform carrier aggregation (CA) ofa cell on the licensed frequency and a cell on the unlicensed frequency,use the cell on the licensed frequency as a primary cell (PCell), anduse the cell on the unlicensed frequency as a secondary cell (SCell). Asalready stated above. LTE-U may be executed using a shared frequency(Shared frequency band, Shared spectrum) allocated to a plurality ofoperators (service providers) instead of using the unlicensed frequency.In this case, LTE-U may be achieved by the aforementioned LAA or ascheme similar to LAA. Alternatively, the LTE-U eNB 1 and the UE 3 mayperform CA using a plurality of shared frequencies (e.g., twofrequencies F3 and F4), and execute normal LTE in a PCell on one of twoshared frequencies (F3) and execute LTE-U in a SCell on the other sharedfrequency (F4). As already stated above, LTE-U using a shared frequencyis specifically referred to as Licensed Shared Access (LSA).Furthermore, the LTE-U eNB 1 and the UE 3 may perform CA using a sharedfrequency allocated to a plurality of operators (e.g., F3) and anunlicensed frequency in a narrow sense that is not allocated to anyoperator (e.g., F2 (e.g., 5 GHz band)), and execute normal LTE in aPCell on the shared frequency (F3) and execute LTE-U in a SCell on theunlicensed frequency in a narrow sense (F2).

Further, in the plurality of embodiments including this embodiment, itis assumed that communication on the unlicensed frequency (or the sharedfrequency) executed in LTE-U is basically downlink data transmissionfrom the radio base station 1 to the radio terminal 3 in order tosimplify explanation. Needless to say, however, communication on theunlicensed frequency (or the shared frequency) according to LTE-U can beapplied also to uplink data transmission from the radio terminal 3 tothe radio base station 1. Further, when the communication between theradio base station 1 and the radio terminal 3 on the unlicensedfrequency can be performed only in the downlink, in LAA using theunlicensed frequency as the secondary cell (SCell), the unlicensedfrequency does not substantially serve as a separate cell and onlyserves as a downlink secondary carrier (Secondary Component Carrier:SCC). In the plurality of embodiments including this embodiment,however, explanation will be basically given without considering whetherthe unlicensed frequency serves as a separate cell on its own and asupplementary explanation will be given as necessary.

FIG. 3 is a sequence diagram showing operations of the radio basestation (LTE-U eNB) 1 and the radio terminal (UE) 3 according to thefirst embodiment. The radio terminal 3 is denoted as “UE #1” in FIG. 3.In FIG. 3, it is assumed that the LTE-U eNB 1 manages a cell (Cell #1)on the licensed frequency (F1) and a cell (Cell #2) on the unlicensedfrequency (F2).

In FIG. 3, the UE 3 first establishes a radio connection with the LTE-UeNB 1 in the Cell #1 (RRC Connection Establishment, S101) and furtherestablishes a bearer (e.g., EPS bearer, E-RAB) with a core network (EPC)(not shown). Then, the UE 3 enters a state in which, for example, the UE3 can transmit and receive user data (not shown). The LTE-U eNB 1instructs the UE 3 to perform terminal measurement (UE measurement) onthe unlicensed frequency (e.g., F2), by means of a predetermined controlsignaling in the Cell #1 (Measurement Configuration and Instruction forUnlicensed Frequency (e.g., Cell #2 on F2), S102). In other words, thepredetermined control signaling transmitted in the Cell #1 explicitly orimplicitly indicates an instruction for the terminal measurement (UEmeasurement) on the unlicensed frequency (e.g., F2).

The control signaling or the instruction for the terminal measurement(S102) is associated with at least one of: a measurement timingindicating a timing when the UE 3 should perform the terminalmeasurement on the unlicensed frequency (e.g., the Cell #2 of F2) (i.e.,a timing when the UE 3 shall perform the terminal measurement); and ameasurement period indicating a period in which the UE 3 should performthe terminal measurement (i.e., an appropriate period in which theterminal measurement is executed). In other words, the control signalingor the instruction for the terminal measurement (S102) explicitly orimplicitly indicates at least one of the measurement timing and themeasurement period (measurable period) of the terminal measurement to beperformed by the UE 3 on the unlicensed frequency (e.g., the Cell #2 ofF2). For example, the instruction for the terminal measurement mayexplicitly indicate at least one of the measurement timing and themeasurement period or may include information regarding at least one ofthe measurement timing and the measurement period. Further, theinstruction for the terminal measurement may include informationregarding one or both of the unlicensed frequency and the cell on theunlicensed frequency, on which the terminal measurement is to beperformed. Further, the number of unlicensed frequencies on which theterminal measurement is to be performed may be one, as shown in FIG. 3,or may be two or more. In a similar way, the number of cells on theunlicensed frequency(ies) may be one or may be two or more.Configuration information for the terminal measurement (MeasurementConfiguration: MeasConfig) and the instruction for the terminalmeasurement (Measurement Instruction) may be transmitted by the samecontrol signaling or may be transmitted by different control signalings(or by a control message and control signaling).

The configuration information for the terminal measurement (MeasConfig)includes, for example, at least one of: information regarding one ormore unlicensed frequencies on which the terminal measurement to beperformed; and information regarding cell(s) on these unlicensedfrequency(ies). The information regarding the unlicensed frequency(ies)may include, for example, one or any combination of the followingelements:

-   -   a frequency identifier of LTE (e.g., E-UTRA Absolute Radio        Frequency Channel Number (EARFCN)):    -   an unlicensed frequency identifier (e.g., an Unlicensed        frequency index); and    -   a (center) frequency (e.g., a carrier frequency).

The unlicensed frequency identifier may be defined as a number or anindex newly added to an unlicensed frequency that is available forLTE-U.

The information regarding the cell(s) on an unlicensed frequency(ies)may include, for example, one or any combination of the followingelements:

-   -   a cell identifier (e.g., a Physical Cell Identifier (PCI), an        EUTRAN Cell Global ID (ECGI), or a Virtual Cell ID); and    -   an unlicensed frequency cell identifier (e.g., an Unlicensed        Cell ID).

The Virtual Cell ID may be, for example, a scrambling code identifier(e.g., a Scrambling Identity or a Scrambling Code ID) used to transmit areference signal or another signal in the cell on the unlicensedfrequency. The unlicensed frequency cell identifier may be defined as acell number or a cell index newly added to a cell on an unlicensedfrequency.

Further, MeasConfig may include another network identifier (e.g., aPublic Land Mobile Network Identifier (PLMN ID), a Tracking AreaIdentity (TAI), or a Tracking Area Code (TAC)). When MeasConfig includesthese network identifiers, the radio terminal 3 may perform the terminalmeasurement in a cell in response to detecting the specified networkidentifier in this cell.

Furthermore, MeasConfig may include information regarding othersystem(s) on the unlicensed frequency on which the terminal measurementis to be performed. The information regarding other system(s) may be,for example, a WLAN (Access Point) identifier (e.g., a Service SetIdentifier (SSID), a Basic SSID (BSSID), or a Homogenous Extended SSID(HESSID)). When MeasConfig includes the WLAN identifier, the radioterminal 3 may measure reception quality (e.g., a Received SignalStrength Indicator (RSSI), a Received Channel Power Indicator (RCPI) ora Received Signal to Noise Indicator (RSNI)) of a signal from the WLANin response detecting the specified WLAN identifier on the unlicensedfrequency on which the terminal measurement is to be performed, andreport the measured reception quality to the radio base station 1.

With reference once again to FIG. 3, the explanation will be continued.The UE 3 performs the terminal measurement in the Cell #2 in response tothe control signaling (S102), that is, in accordance with theinstruction for the terminal measurement (Measurement, S104) and reportsthe result of the terminal measurement to the LTE-U eNB in the Cell #1(Measurement Reporting for Unlicensed Frequency (e.g., Cell #2 on F2),S105). In the terminal measurement (S104), the UE 3 may measure, forexample, reception intensity or reception quality of a reference signal(S103) transmitted from the LTE-U eNB 1 in the Cell #2. The terminalmeasurement and the terminal measurement report may be performed notonly in the cell (Cell #2) on the unlicensed frequency (F2) but also inother cell(s) on F2, in other unlicensed frequency(ies), or in thelicensed frequency. The instruction for the terminal measurement may beexplicitly transmitted, or the transmission of the aforementionedinformation regarding the terminal measurement timing or the measurementperiod may be an implicit instruction for performing the terminalmeasurement.

As described above, the radio base station (LTE-U eNB) 1 notifies orinstructs the radio terminal (UE) 3 of one or both of the measurementtiming and the measurement period of the terminal measurement on theunlicensed frequency and, the fore, can collect a desired result of theterminal measurement. The LTE-U eNB 1 also can determine whether it ispossible (or appropriate) to communicate with the UE 3 (i.e., performdata transmission/reception by LTE) (in a cell) on the unlicensedfrequency based on the result of the terminal measurement.

However, the radio base station (LTE-U eNB) 1 is not always able tooperate LTE (in a cell) on the unlicensed frequency. The LTE-U eNB 1 maycheck whether the unlicensed frequency is available for LTE-U by sensingor the like and, for example, transmit a synchronization signal and areference signal when the unlicensed frequency is available for LTE-U.Therefore, the LTE-U eNB 1 may adjust the transmission timing of thecontrol signaling or adjust control information carried by the controlsignaling, which indicates at least one of the measurement timing andthe measurement period, in such a way that the measurement timing or themeasurement period of the terminal measurement on the unlicensedfrequency is within the period in which the LTE-U eNB 1 can use theunlicensed frequency (i.e., availability period). In one example, theLTE-U eNB 1 may specify one or both of the measurement timing and themeasurement period in such a way that they are within the period inwhich the unlicensed frequency is determined to be available. Further,when it is determined that the unlicensed frequency is available orwhile the unlicensed frequency is available, the LTE-U eNB 1 maytransmit the instruction for the terminal measurement on the unlicensedfrequency by the predetermined control signaling. As already statedabove, the aforementioned sensing by the LTE-U eNB 1 is also referred toas Listen Before Talk (LBT). This sensing corresponds, for example, toCAC for radar systems or CCA executed by a WLAN AP. The CAC is notrequired to be executed when the unlicensed frequency to be measured isnot a frequency used in radar systems.

Specific Example 1

A specific example 1 according to the first embodiment will bedescribed. FIG. 4 is a sequence diagram showing operations of the radiobase station (LTE-U eNB) 1 and the radio terminal 3 in the specificexample 1. The case assumed in FIG. 4 is similar to that assumed in FIG.3: the radio base station (LTE-U eNB) 1 manages a cell (Cell #1) on thelicensed frequency (F1) and a cell (Cell #2) on the unlicensed frequency(F2). The LTE-U eNB 1 instructs the UE 3 to perform terminal measurementon the unlicensed frequency (F2) and determines whether to performcommunication with the UE 3 according to LTE-U on the unlicensedfrequency (e.g., downlink data transmission) based on the result of theterminal measurement. The radio terminal 3 is denoted as “UE #1” in FIG.4.

In FIG. 4, the UE 3 first establishes a radio connection with the LTE-UeNB 1 in the Cell #1 (RRC Connection Establishment, S201) and furtherestablishes a bearer (e.g., EPS bearer, E-RAB) with a core network (EPC)(not shown). Then, the UE 3 enters a state in which, for example, the UE3 can transmit and receive user data (not shown). The LTE-U eNB 1performs first sensing on the unlicensed frequency (F2) (Perform firstchannel sensing. S202). The first sensing includes CAC for radarsystems, CCA for other systems such as WLAN, CCA for LTE-U served byother operators (service providers), or two of them, or all of them.Upon determining that the unlicensed frequency (F2) is available by thefirst sensing (S202), the LTE-U eNB 1 instructs the UE 3 to perform theterminal measurement (in the cell (Cell #2)) on F2 by a predeterminedcontrol signaling, and then the UE 3 performs the terminal measurementin accordance with the instruction and reports the result of theterminal measurement to the LTE-U eNB 1 (Measurement Configuration,Instruction and Reporting for Unlicensed Frequency, S203). The LTE-U eNB1 determines whether to perform communication (e.g., downlink datatransmission) with the UE 3 in the Cell #2 based on the result of theterminal measurement that has been reported (S204).

The terminal measurement may include, for example, measurement ofreception quality of a reference signal (RS) (e.g., Reference SignalReceived Power (RSRP), Reference Signal Received Quality (RSRQ), anRSSI, a Channel Quality Indicator (CQI), or aSignal-to-Interference-plus-Noise ratio (SINR)). The determination madeby the LTE-U eNB 1 may be performed based on whether the value of thereception quality that has been reported is equal to or larger than apredetermined value (or larger than the predetermined value). Thereference signal is a generic name for signals whose types and sequencesor candidates thereof are known in advance in the radio terminal 3 andis also referred to as a pilot signal. The reference signal in LTEincludes, for example, a Cell Specific Reference Signal (CRS) that isdifferent per cell, a Channel State Information (CSI) RS that is usedalso for a CQI measurement, or a discovery reference signal (DRS) thatis used for cell detection.

Further or alternatively, the terminal measurement may includemeasurement of reception quality (RSSI, RCPI, or RSNI) of apredetermined signal defined in other systems such as WLAN (e.g., areference signal or some or all of the signals transmitted in thefrequency of this system). In this case, the determination made by theLTE-U eNB 1 may be performed based on whether the value of the receptionquality that has been reported is equal to or smaller than apredetermined value (or smaller than the predetermined value).Alternatively, the UE 3 may perform detection (i.e., attempt to performdetection) of signals of another system such as WLAN by the terminalmeasurement and report the result of the detection. In this case, thedetermination made by the LTE-U eNB 1 may be performed based on whetherthe LTE-U eNB 1 receives the report indicating that other system(s) hasbeen detected.

Further or alternatively, the UE 3 may acquire load information (BasicService Set (BSS) Load) on other system(s) such as WLAN in the terminalmeasurement and report the load information. In this case, thedetermination made by the LTE-U eNB 1 may be performed based on whetherthe load of the other system(s) is equal to or larger than apredetermined threshold (or larger than the threshold). The LTE-U eNB 1may determine whether to perform communication with the UE 3 in the Cell#2 based on the aforementioned plurality of results of the terminalmeasurement.

When the LTE-U eNB 1 determines to perform communication with the UE 3in the Cell #2, the LTE-U eNB 1 transmits, to the UE 3 in the Cell #1,radio resource configuration information regarding the Cell #2 (e.g.,RadioResourceConfigCommon and RadioResourceConfigDedicated) (RadioResource Configuration for Cell #2, S205). In this case, the LTE-U eNB 1may use, for example, an RRC Connection Reconfiguration message.

The LTE-U eNB 1 then performs second sensing on the unlicensed frequency(F2) (Perform second channel sensing, S206). The second sensing may bethe same as, or different from, the first sensing. When the LTE-U eNB 1determines that the unlicensed frequency (F2) is available, the LTE-UeNB 1 transmits user data (UP data) to the UE 3 in the Cell #2 (S207).In this case, scheduling of the user data (i.e., transmission ofinformation regarding allocation of radio resources) may be performed ina cell (e.g., the Cell #1) on the licensed frequency (e.g., F1) or inthe Cell #2. The former scheduling may use the technique referred to ascross-carrier scheduling in LTE. Alternatively, the user datatransmission to the UE 3 in the Cell #2 may be performed based on CSIfeedback information (e.g., CQI, Precoding Matrix Indicator (PMI), RankIndicator (RI)) regarding the Cell #2 reported from the UE 3 in the Cell#1.

Using the aforementioned procedure, the radio base station (LTE-U eNB) 1is able to appropriately determine the radio terminal (UE) 3 that isallowed to perform LTE (LTE-U) on the unlicensed frequency. As a result,it can be expected to improve performance (e.g., system throughput) ofthe whole LTE radio communication system.

Specific Example 2

A specific example 2 according to the first embodiment will bedescribed. The difference from the specific example is that the radiobase station (LTE-U eNB) 1 uses control signaling that is generatedusing control information defined for instructing the terminalmeasurement on the unlicensed frequency. The control information may beexplicitly contained in the control signaling, or the controlinformation may be used for data scrambling in the process of generatingthe control signaling. In the specific example 2, a Layer 1 (L1) controlsignal or a Layer 2 (L2) control signal or both (L1/L2 signaling)transmitted in a physical downlink control channel (PDCCH) is used asthe control signaling to transmit the instruction for the terminalmeasurement on the unlicensed frequency (F2). The control information isa U-RNTI (an LTE-U RNTI, a U-LTE RNTI, or an Unlicensed RNTI), which isone of the identifiers (Radio Network Temporary Identifier: RNTI) usedfor generation and detection of the PDCCH. The U-RNTI may be set to acommon value for a plurality of radio terminals 3 that are in the radioconnected state (RRC_CONNECTED) in a cell on the licensed frequency(e.g., F1) (i.e., radio terminals having the capability of communicatingon the unlicensed frequency).

That is, the control signaling (L1/L2 control signal) that transmits theinstruction for the terminal measurement on the unlicensed frequency(F2) is transmitted using the U-RNTI (i.e., its Cyclic Redundancy Check(CRC) part is scrambled by the U-RNTI). In one example a new PDCCHformat (a Downlink Control Information (DCI) format) may be defined forthe instruction for the terminal measurement on the unlicensedfrequency. Alternatively, a new physical control channel named “LTE-UPDCCH (U-PDCCH)” may be defined, and this U-PDCCH may be used fortransmission of the L1/L2 control signal in place of the PDCCH. TheU-PDCCH may be defined, for example, to use a part of the resources fora physical downlink shared data channel (PDSCH).

In the specific example 2, the reception of the control signaling by theradio terminal (UE 3) implicitly indicates the measurement timing. Thatis, when the radio terminal (UE) 3 receives the control signaling, theradio terminal (UE) 3 recognizes that it has received an instruction forperforming the terminal measurement in the cell (Cell #2) on theunlicensed frequency (F2). In order to achieve this process, the radiobase station (LTE-U eNB) 1 may send the configuration information (e.g.,Measurement Configuration: MeasConfig), which is necessary for theterminal measurement in the cell (Cell #2) on the unlicensed frequency(F2), to the radio terminal (UE) 3 in the cell (Cell #1) on the licensedfrequency (F1) in advance by using an RRC signaling.

MeasConfig includes, for example, at least one of: information regardingone or more unlicensed frequencies (F2) to be measured (e.g., EARFCN,Unlicensed frequency index, or carrier frequency); and informationregarding a cell(s) (Cell #2) on the unlicensed frequency (F2) (e.g.,PCI, ECGI, Virtual Cell ID, Unlicensed Cell ID). Furthermore, the radiobase station (LTE-U eNB) 1 may notify, using MeasConfig or another RRCinformation element (IE), the radio terminal (UE) of informationregarding a period allowed for allocation of the unlicensed frequency toLTE-U. The information regarding the period allowed for allocation mayinclude one or both a Duty Cycle Period (e.g., in millisecond (ms)) anda Duty Cycle (e.g., in percent (%)). The Duty Cycle Period is thereference period to define the period allowed for allocation. The DutyCycle indicates the rate of the period allowed for allocation in thereference period. When the Duty Cycle Period is 200 ms and the DutyCycle is 50%, for example, it may be considered that the period allowedfor allocation to LTE-U of 100 ms is provided for every 200 ms. Thevalues of the Duty Cycle Period and the Duty Cycle may be defined, forexample, in advance in the specification, or may be sent from a controlapparatus (e.g., a Mobility Management Entity (MME), or an Operation,Administration and Maintenance (OAM) entity) to the radio base station1. Otherwise, the radio base station 1 itself may determine the DutyCycle Period and the Duty Cycle as appropriate based on the result ofsensing or the like.

FIG. 5 is a diagram for describing the terminal measurement performed bythe radio terminal (UE) 3 in the cell (Cell #2) on the unlicensedfrequency (F2) according to the specific example 2. In this example, theradio base station (LTE-U eNB) 1 dynamically switches the operationstate of the Cell #2 based on, for example, the result of sensing forother systems. For example, the LTE-U eNB 1 intermittently transmits apredetermined reference signal (RS) on F2 so as to switch the Cell #2 On(i.e., in operation) and Off (i.e., not in operation). The period inwhich the predetermined reference signal (RS) is being transmitted on F2corresponds to the On (in operation) period in the Cell #2.

When the LTE-U eNB 1 determines that the Cell #2 should be switched on,the LTE-U eNB 1 transmits the control signaling (L1/L2 control signal),which is transmitted by (U-)PDCCH using the aforementioned U-RNTI, inthe cell (e.g., the Cell #1) on the licensed frequency to instruct theUE 3 to perform the terminal measurement in the Cell #2. Upon receivingthe control signaling, the UE 3 performs the terminal measurement in theCell #2.

There are three methods shown in FIG. 5, for example, as a method of theterminal measurement in the Cell #2. In the first method (option 1),after receiving the (U-)PDCCH, the UE3 performs the terminal measurementfor a predetermined RS in the Cell #2 only once. In this method, the UE3 performs the terminal measurement only once just after receiving the(U-)PDCCH (e.g., after several ms) and the UE 3 can immediately send theterminal measurement report, whereby it is possible to immediately usethe Cell #2 (if a criterion for communicating in the Cell #2 issatisfied).

In the second method (option 2), after receiving the (U-)PDCCH, the UE 3performs the terminal measurement for a predetermined RS in the Cell #2a plurality of times. For example, the UE 3 may perform a primaryterminal measurement (i.e., L1 measurement in this example) of two ormore measurements (i.e., two or more measurement samples), which is arequirement for the terminal measurement used for cell (re)selection orthe like in LTE, and perform averaging process (i.e., L3 filtering) onthe results of the primary terminal measurement (secondary terminalmeasurement). This method is advantageous over the first method in thatreliability (accuracy) of the result of the terminal measurementincreases. However, according to the requirements for the terminalmeasurement used for the cell (re)selection or the like, it is requiredto perform two measurements in about 200 ms. Thus, time restrictions arerelatively loose. Therefore, when this terminal easement is reused forLTE-U, it is preferable that the requirements for the period in whichthe primary terminal measurement (L1 measurement) of two (or more)measurements is performed be defined to be, for example, within about 10milliseconds or within several tens of milliseconds. The term “terminalmeasurement” means, but not limited to, both the primary terminalmeasurement and the secondary terminal measurement mentioned above(i.e., both the primary terminal measurement and the secondary terminalmeasurement is performed).

In the third method (option 3), after receiving the (U-)PDCCH, the UE 3starts and continues the terminal measurement during a period in whichthe UE 3 can be detecting a predetermined signal (i.e., aSynchronization signal (RS) and a Master Information Block (MIB))transmitted in the Cell #2, and the UE 3 suspends (or stops) theterminal measurement when the UE 3 cannot detect the predeterminedsignal any more. Here, the “period in which the UE 3 can be detectingthe predetermined signal” can also be referred to as a “period in whichthe UE 3 can be detecting the Cell #2”. The period in which the UE 3 canbe detecting the predetermined signal may be, for example, a periodduring which reception quality (e.g., RSRP) of a predetermined RS (e.g.,CRS) is equal to or larger than a predetermined threshold (e.g., −110dBm). One advantage of this method is that reliability (accuracy) of theresult of the terminal measurement further increases compared to that ofthe second method. On the other hand, it is required to set a conditionfor continuing the terminal measurement (or a condition for suspendingthe terminal measurement) in the UE 3 in such a manner that the UE 3does not continue the terminal measurement after the LTE-U eNB 1suspends the transmission of the predetermined RS in the Cell #2.Alternatively, the maximum number of times or the longest durationperiod of the terminal measurement may be defined in the specificationin advance, or may be sent to the UE 3 from the LTE-U eNB 1.

Furthermore, when the UE 3 has received the information regarding theperiod allowed for allocation of the unlicensed frequency to LTE-U(e.g., the Duty Cycle Period and the Duty Cycle) in advance, the UE 3may determine the duration period of the terminal measurement based onthis information. When the Duty Cycle Period is specified to be 100 msand the Duty Cycle is specified to be 40%, for example, 40 ms in a cycleof 100 ms corresponds to the period allowed for allocation. When the UE3 detects a predetermined signal (e.g., RS) in the Cell #2, the UE 3 maystart the terminal measurement for the period of 40 ms at the time(e.g., subframe number (subframe #)) when the predetermined signal isdetected. Furthermore, the UE 3 may repeat the same operation in a cycleof 100 ms. That is, the UE 3 may suspend the terminal measurement forthe period of 60 ms after the terminal measurement performed in thefirst 40 ms and resume the terminal measurement during the next 40 ms.

The U-RNTI may be common for all the radio terminals 3 in the cell inwhich the radio terminal resides (serving cell: e.g., Cell #1 in thespecific example 2), may be common for some of the radio terminals 3(terminal group) in the cell, or may be different for each radioterminal 3.

Further, the LTE-U eNB 1 may transmit (U-)PDCCH when the LTE-U eNB 1 isturning on the cell (e.g., the Cell #2) on the unlicensed frequency(e.g., F2) (i.e., when the LTE-U eNB 1 starts transmitting apredetermined signal (e.g., Synchronization signal (RS) and MIB)), ormay transmit (U-)PDCCH at a desired timing during a period in which thecell is in the On state.

Modified Example of Specific Example 2

A modified example of the aforementioned specific example 2 will bedescribed. The difference from the specific example 2 is that the(U-)PDCCH, which is generated by using U-RNTI and indicates theinstruction for the terminal measurement in the cell (Cell #2) on theunlicensed frequency (F2), includes the information regarding themeasurement period in which the terminal measurement should beperformed. That is, upon determining that the Cell #2 should be switchedon, the radio base station (LTE-U eNB) 1 transmits the (U-)PDCCH usingthe U-RNTI in the cell (e.g., Cell #1) on the licensed frequency (e.g.,F) to instruct the UE 3 to perform the terminal measurement in the Cell#2. Upon receiving the (U-)PDCCH, the UE 3 starts the terminalmeasurement in the Cell #2, continues the terminal measurement in theCell #2 for the measurement period that has been instructed, and reportsthe result to the LTE-U eNB 1 in the cell (e.g., Cell #1) on thelicensed frequency. In this method, the LTE-U eNB can collectappropriate result of the terminal measurement which provides desiredreliability (or accuracy).

The information regarding the measurement period includes, for example,the following items:

-   -   a combination of a start timing and an end timing of the        terminal measurement;    -   an end timing of the terminal measurement;    -   a period of the terminal measurement: or    -   information regarding the period allowed for allocation of the        unlicensed frequency to LTE-U.

As described above, the information regarding the period allowed forallocation may include one or both the Duty Cycle Period (e.g., inmillisecond (ms)), which is the reference period to define the periodallowed for allocation, and the Duty Cycle (e.g., in percent (%)), whichindicates the rate of the period allowed for allocation in the referenceperiod. That is, the Duty Cycle Period and the Duty Cycle can be used tospecify the cycle and the length (duration) of the periodic periodallowed for allocation.

The method of the terminal measurement in the Cell #2 may vary dependingon the information regarding the measurement period. For example, whenthe information regarding the measurement period indicates thecombination of the start timing and the end timing of the terminalmeasurement the radio terminal 3 may start and end the terminalmeasurement in accordance with the indicated start timing and endtiming. When the information regarding the measurement period indicatesthe end timing of the terminal measurement, the radio terminal 3 maystart the terminal measurement in response to receiving the controlsignaling (L1/L2 control signal) including the information regarding themeasurement period and end the terminal measurement in the indicated endtiming. When the information regarding the measurement period indicatesthe period of the terminal measurement, the radio terminal 3 maycontinue the terminal measurement from the time the control signaling isreceived to the time this period expires.

Further, in the aforementioned information regarding the measurementperiod, the start timing, the end timing, the period of the terminalmeasurement, and the information regarding the period allowed forallocation may be defined using one or any combination of the followingelements:

-   -   a unit time (ms);    -   a subframe number (subframe #) or a frame number (SFN):    -   the number of subframes or the number of frames;    -   a subframe pattern or a frame pattern;    -   a subframe offset or a frame offset;    -   an absolute time;    -   a relative time; and    -   a rate (%).

The unit time may be indicated by, for example, us (microsecond) or s(second), instead of ms (millisecond). For example in LTE, the subframenumber (subframe #) can be any value 0 (#0) to 9 (#9) and each subframehas a length of 1 ms. The frame number is, for example, a System FrameNumber (SFN) in LTE, which can be any value 0 (#0) to 1023 (#1023). Eachframe consists of 10 subframes (10 ms). The subframe offset or the frameoffset specifies the time point that is deviated from the beginning(i.e., #0) of the subframe or the frame by the offset value, and iseffective, for example, for specifying the start timing of the terminalmeasurement.

The subframe pattern or the frame pattern indicates subframe(s) orframe(s) in which the terminal measurement is performed and may be a bitsequence (bitmap) that represents 10 subframes or 10 frames. Forexample, in the bit sequence, the bit(s) corresponding to subframe(s) orframe(s) in which the terminal measurement should be performed may beset to 1 (or 0) and the remaining bit(s) may be set to 0 (or 1).

The absolute time is, for example, time information acquired by a GlobalNavigation Satellite System (GNSS) such as a Global Positioning System(GPS), and may be used to specify one or both the start timing and theend timing of the terminal measurement. The relative time may indicatean elapsed time since the reception of the control signaling includingthe information regarding the measurement period (subframe) or since thedetection (restoration) of the control signaling, and may be used tospecify the period in which the terminal measurement is performed.

The rate is used, for example, to indicate the Duty Cycle included inthe information regarding the period allowed for allocation of theunlicensed frequency to LTE-U. That is, the rate can be used to specifythe length (duration) of the periodic period allowed for allocation. Therate with respect to the period allowed for allocation may be definedby, for example, a fractional value (0.01, 0.02, . . . , 010, . . . ,0.99, or 1.00), rather than percentage (%). Further, when the maximumvalue of the Duty Cycle Period is denoted by MaxDutyCycle, the value ofthe rate (i.e., it corresponds to the Duty Cycle) may be indicated by aninteger value (1, 2, . . . , MaxDutyCycle). In this case, the value ofthe rate substantially indicates the length of the ON period of the DutyCycle, i.e., the length of the period allowed for allocation of theunlicensed frequency to LTE-U.

They are merely examples and the parameters that have been describedabove may be used in other methods. Further or alternatively, theinformation regarding the measurement period may include otherparameters.

More particularly, when the information regarding the measurement periodindicates one or both the start timing and the end timing of theterminal measurement, each of the start timing and the end timing may beexpressed by the unit time (ms). The radio base station 1 mayrespectively specify, for example, “xx” and “yy” in (the fields of) thecontrol information specifying the start timing and the end timing, andthe radio terminal 3 may start the terminal measurement xx (ms) afterthe timing when it has received the control signaling including thisinformation (i.e., time of reception or time when the reception has beendetected) and may end the terminal measurement after yy (ms) elapses.Instead, when each of the start timing and the end timing is expressedby the subframe number, the radio base station 1 may specify, forexample, “n” and “m” for (the fields of) the control information thatspecifies the start timing and the end timing, respectively, and theradio terminal 3 may start the terminal measurement from the subframe #njust after the control signaling including this information is received(i.e., the subframe at which it has been received or the subframe atwhich the reception has been detected) and continuously perform theterminal measurement until the subframe #m. The same is applicable to acase in which the frame number is used in place of the subframe number.Instead, when each of the start timing and the end timing is expressedby the absolute time, the radio base station 1 may specify the absolutetime indicating the start timing or the end timing and the radioterminal may start or end the terminal measurement at the absolute time.

When the information regarding the measurement period indicates theperiod of the terminal measurement, this period may be expressed by theunit time (ms). The radio base station 1 may specify, for example, “zz”for (the field of) the control information that specifies this periodand the radio terminal 3 may perform the terminal measurement during theperiod of zz (ms) from the timing when it has received the controlsignaling including this information (i.e., time of reception or timewhen the reception has been detected). Instead, when the period of theterminal measurement is expressed by the number of subframes, the radiobase station 1 may specify “N” for (the field of) the controlinformation that specifies this period and the radio terminal 3 mayperform the terminal measurement during the period of N subframes fromthe timing when it has received the control signaling including thisinformation (i.e., the subframe at which it has been received or thesubframe at which the reception has been detected). Instead, when theperiod of the terminal measurement is expressed by the subframe pattern,the radio base station 1 may specify a 10-bit bitmap (e.g.,“0000001111”) for (the field of) the control information that specifiesthis period and the radio terminal 3 performs the terminal measurementin a subframe # corresponding to “1” in the bitmap based on the timingwhen it has received the control signaling including this information(i.e., the subframe at which it has been received or the subframe atwhich the reception has been detected). For example, when the controlsignaling is received in the subframe #2, the LSB (left end) of the10-bit bitmap corresponds to the subframe #2 and the following bitscorrespond to the subframes #3, #4, #5, #6, #7, #8, #9, #0, and #1 inthis order. Alternatively, each of the bits of the bitmap may be fixedlyallocated to the subframes #0, #1, #2, . . . , #9 from the LSB inadvance. In this case, the bitmap shown above indicates that thesubframes #6, #7, #8, and #9 correspond to the measurement period.

Furthermore, in order to specify the period of the terminal measurement,both the subframe pattern and the subframe offset (start offset) may beused. The radio base station 1 may use the subframe offset to specify,for example, subframe number (subframe #) corresponding to the LSB (leftend) of the 10-bit bitmap. When the start offset is set to be 5 in theaforementioned example of the 10-bit bitmap, the LSB corresponds to thesubframe #5 and the following bits correspond to the subframes #6, #7,#8. #9, #0, #1, #2, #3, and #4 in this order. The subframe pattern maybe expressed by a bitmap having another number of bits (e.g., successive40 subframes in a 40-bit bitmap) or may be expressed by another dataformat (e.g., a list of subframes (#) corresponding to the terminalmeasurement period). The same is applicable also to a case in which theframe pattern is used in place of the subframe pattern. The frame offsetmay be additionally used. The frame pattern may also be expressed by thebitmap or by another data format.

Note that the information regarding the measurement period and thespecific data format for indicating this information in theaforementioned examples are merely examples and another combination canbe used.

Specific Example 3

A specific example 3 according to the first embodiment will bedescribed. The difference from the specific example 2 is that an L2control signal (MAC signaling) including control information (MACControl Element: MAC CE) of a Media Access Control (MAC) layertransmitted in the downlink shared channel (DL-SCH) is used as thecontrol signaling that transmits the instruction for the terminalmeasurement on the unlicensed frequency (F2). In the control signaling,an Unlicensed Band Measurement MAC CE (or may be another name such as anUnlicensed Frequency Measurement MAC CE, an Unlicensed SpectrumMeasurement MAC CE, an LTE-U MAC CE or the like) is used as the controlinformation defined for the instruction for the terminal measurement onthe unlicensed frequency. A new value of an identifier (Logical ChannelIdentity: LCID) used for generation and restoration of a MAC Sub headercorresponding to the Unlicensed Band Measurement MAC CE may be defined(e.g., LCID Index=11xxx (e.g., 11001) for DL-SCH).

In the specific example 3, when the radio terminal (UE) 3 receives thecontrol signaling (MAC signaling) and successfully detects (restores)the Unlicensed Band Measurement MAC CE, the radio terminal (UE) 3recognizes that it has been instructed to perform the terminalmeasurement in the cell (Cell #2) on the unlicensed frequency (F2). Inorder to achieve this process, the radio base station (LTE-U eNB) 1 maysend, to the radio terminal (UE) 3 in the cell (Cell #1) on the licensedfrequency (F1) in advance using for example an RRC signaling, theconfiguration information (Measurement Configuration: MeasConfig) thatis necessary for the terminal measurement for the cell (Cell #2) on theunlicensed frequency (F2).

Further, the Unlicensed Band Measurement MAC CE includes informationregarding the measurement period of the terminal measurement on theunlicensed frequency (e.g., F2). The information regarding themeasurement period may be similar to or different from the informationdescribed in the modified example of the specific example 2.

FIG. 6 is a diagram for describing the terminal measurement performed bythe radio terminal (UE) 3 in the cell (Cell #2) on the unlicensedfrequency (F2) according to the specific example 3. Similar to FIG. 5related to the specific example 2, in the specific example 3, the radiobase station (LTE-U eNB) 1 dynamically switches the operation state ofthe Cell #2 based on, for example, the result of sensing for othersystems. When the LTE-U eNB 1 determines that the Cell #2 should beswitched on, the LTE-U eNB 1 transmits the control signaling (MACsignaling) including the aforementioned Unlicensed Band Measurement MACCE in the cell (e.g., Cell #1) on the licensed frequency to instruct theUE 3 to perform the terminal measurement in the Cell #2. Upon receivingthe control signaling, the UE 3 performs the terminal measurement in theCell #2. In this example, the control signaling includes the informationregarding the measurement period and the UE 3 performs the terminalmeasurement in accordance with this information.

Similar to the description in the modified example of the specificexample 2, the method of the terminal measurement in the Cell #2 mayvary depending on the information regarding the measurement period. Inthe specific example 3, however, the control signaling (MAC signaling)is different from that of the modified example of the specific example2, so that the operation in the specific example 3 is not the same asthat in the specific example 2. For example, when the start timing ofthe terminal measurement is not explicitly specified, the terminalmeasurement may be started in response to the control information(Unlicensed Band Measurement MAC CE) transmitted in the controlsignaling being successfully detected (decoded) in the UE 3.Alternatively, the start point of the measurement period (measurableperiod) of the terminal measurement may be set to the time point atwhich the control information (Unlicensed Band Measurement MAC CE)transmitted by the control signaling has been successfully detected(decoded) in the UE 3.

Specific Example 4

A specific example 4 according to the first embodiment will bedescribed. The difference from the specific examples 1-3 is that theradio terminal (UE) 3 performs the terminal measurement (in the cell(Cell #2)) on the unlicensed frequency (F2) as specified in advance.Specifically, the radio base station (LTE-U eNB) 1 transmits, to theradio terminal (UE) 3 by an RRC signaling or the like in advance, theconfiguration information (Measurement Configuration: MeasConfig) thatis necessary for the terminal measurement in the cell (Cell #2) on theunlicensed frequency (F2). Further, the LTE-U eNB 1 includes, in theMeasConfig, configuration information about a terminal measurement gapused for the terminal measurement (Measurement Gap Configuration:MeasGapConfig)

In the specific example 4, similar to the specific example 2, the L1/L2control signal transmitted in the physical downlink control channel(PDCCH or the aforementioned U-PDCCH) is used as the control signalingthat transmits the instruction for the terminal measurement on theunlicensed frequency (F2). The control signaling (L1/L2 control signal)is transmitted using the aforementioned U-RNTI. Further, in the specificexample 4, this control signaling includes an instruction for executionof the terminal measurement gap (i.e., an instruction for activation ofthe terminal measurement gap). The instruction for execution of theterminal measurement gap corresponds to the information regarding themeasurement period. The instruction for execution of the terminalmeasurement gap may instruct, for example, execution of the terminalmeasurement in accordance with MeasGapConfig that has been transmitted(specified) in advance. Further, when the LTE-U eNB 1 notifies the UE 3of a plurality of MeasGapConfigs (i.e., patterns of the terminalmeasurement gap) in advance, the instruction for execution of theterminal measurement gap may indicate one of the MeasGapConfigs withwhich the terminal measurement should be executed.

FIG. 7 is a diagram for describing the terminal measurement by the radioterminal (UE) 3 in the cell (Cell #2) on the unlicensed frequency (F2)according to the specific example 4. Similar to FIGS. 5 and 6 accordingto the specific examples 2 and 3, the radio base station (LTE-U eNB) 1dynamically switches the operation state of the Cell #2 based on, forexample, the result of sensing for other systems. The LTE-U eNB 1transmits MeasConfig including MeasGapConfig, in advance, to the UE 3 inthe cell (e.g., the Cell #1) on the licensed frequency. When the LTE-UeNB 1 determines that the Cell #2 should be switched on, the LTE-U eNB 1transmits the control signaling (L1/L2 control signal), which istransmitted by (U-)PDCCH using the aforementioned U-RNTI, in the cell(e.g., the Cell #1) on the licensed frequency to instruct the UE 3 toperform the terminal measurement in the Cell #2. Upon receiving thecontrol signaling, the UE 3 performs the terminal measurement in theCell #2 in accordance with the Measurement Gap specified by theMeasGapConfig.

FIG. 7 shows, as an example, a case in which the length of the terminalmeasurement gap (Measurement Gap Length) is 6 ms. When the UE 3 receivesthe control signaling ((U-)PDCCH) and recognizes that it has receivedthe instruction for performing the terminal measurement in the Cell #2,the UE 3 immediately activates the terminal measurement gap and startsthe terminal measurement. Then the UE 3 executes the terminalmeasurement in the Cell #2 for the period of 6 ms in accordance with theMeasurement Gap Length. The target of the terminal measurement may be aplurality of cells in one unlicensed frequency (F2) or may be aplurality of cells in a plurality of unlicensed frequencies.

Accordingly, it is possible to dynamically execute the terminalmeasurement while maintaining the reliability (accuracy) that isnecessary for the terminal measurement in the cell (Cell #2) on theunlicensed frequency (F2).

FIG. 7 shows an example in which one-shot terminal measurement using theterminal measurement gap (i.e., one-shot terminal measurement for thelength of the terminal measurement gap) is executed every time the radioterminal 3 receives the control signaling (one-shot UE measurement withmeasurement gap). However, the radio terminal 3 may execute the terminalmeasurement using the terminal measurement gap a plurality of times in apredetermined cycle (multiple UE measurements with periodic measurementgap), in response to receiving the control signaling. For example, theradio base station 1 may notify the radio terminal 3 in advance of thenumber of times the terminal measurement using the terminal measurementgap is performed or the period in which the terminal measurement isperformed.

Further, the radio base station 1 may notify the radio terminal 3 inadvance of the configuration information (MeasGapConfig) about theterminal measurement gap of a plurality of patterns and the index tospecify each of the plurality of patterns. The radio base station 1 maysend the control signaling ((U-)PDCCH) indicating the indexcorresponding to the pattern of terminal measurement gap that should beexecuted.

Further, the radio base station 1 may notify the radio terminal 3 of awaiting time (Activation Time) until the radio terminal 3 executes theterminal measurement gap after it receives the control signaling((U-)PDCCH) or a start offset (GapOffset) in the execution of theterminal measurement gap, by using the configuration information aboutthe terminal measurement gap (MeasGapConfig).

Further, the radio base station 1 may specify, by the control signaling,the information regarding the measurement period similar to that in themodified example of the specific example 2. For example, when one orboth of the start timing and the end timing of the terminal measurementis specified, the start timing and the end timing of the terminalmeasurement may respectively indicate the start timing and the endtiming of the terminal measurement gap. Further, when the period of theterminal measurement is specified, this period may indicate the periodin which the terminal measurement gap is effective (i.e., the period inwhich the terminal measurement using the terminal measurement gap isperformed).

Modified Example of Specific Example 4

A modified example of the aforementioned specific example 4 will bedescribed. The difference from the specific example 4 is that thecontrol signaling indicating the instruction for performing the terminalmeasurement in the cell (the Cell #2) on the unlicensed frequency (F2)is an L2 control signal (MAC signaling). This can be achieved, forexample, by adding the information transmitted by (U-)PDCCH described inthe specific example 4 to the Unlicensed Band Measurement MAC CEdescribed in the specific example 3. Since the other details are similarto those in the specific example 4, the descriptions thereof will beomitted.

The aforementioned terminal measurement may be, for example, calculationof an instantaneous measurement value of the reception quality of thereference signal, may be execution of a primary measurement (L1filtering), or may be execution of a secondary measurement (L3filtering). Further, the contents of the terminal measurement in thefollowing descriptions may be different from those stated above.

Second Embodiment

A second embodiment will be described. In this embodiment, prior toexecution of the terminal measurement in a cell on the unlicensedfrequency described in the first embodiment, the radio base station(LTE-U eNB) 1 selects the radio terminal (UE) 3 to which the instructionfor performing the terminal measurement is to be sent. The detailsthereof will be described with reference to FIG. 8. In FIG. 8, the LTE-UeNB 1 manages a cell (Cell #1) on the licensed frequency (F1) and a cell(Cell #2) on the unlicensed frequency (F2). In this embodiment, theradio terminal (UE) 3 has a detection function for detecting proximityto a cell on the unlicensed frequency and a report function forreporting the detection result to the radio base station upon detectionof the proximity. While the following description will be given assuminga case in which the cell on the unlicensed frequency is a non-servingcell for the radio terminal, the cell on the unlicensed frequency may bea serving cell (or a configured cell). The radio terminal 3 is denotedas “UE #1” in FIG. 8.

In FIG. 8, the UE 3 first establishes a radio connection (RRC ConnectionEstablishment) with the LTE-U eNB 1 in the Cell #1 as the serving celland establishes a bearer (e.g., EPS bearer, E-RAB) with a core network(EPC) (not shown). Then, the UE 3 enters a state in which, for example,the UE 3 can transmit and receive user data. The LTE-U eNB 1 performsfirst sensing on the unlicensed frequency (e.g., F2) (Perform firstchannel sensing, S301). The first sensing includes CAC for radarsystems, CCA for other systems such as WLAN, CCA for LTE-U served byother operators (service providers), or two of them, or all of them.

Upon determining that the unlicensed frequency (e.g., F2) is availableby the first sensing (S301), the LTE-UE eNB 1 transmits, to the UE 3 inthe Cell #1, a notification regarding detection of proximity of a cellon the unlicensed frequency (Proximity configuration for unlicensedfrequency, S302). Upon receiving the notification (i.e., in response tothe notification), the UE 3 attempts to detect proximity of the UE 3 toa cell (e.g., the Cell #2) on the unlicensed frequency (e.g., F2) (i.e.,enables (activates) the detection function). When the UE 3 hassuccessfully detected a non-serving cell on the unlicensed frequency(Proximity detection on unlicensed frequency (cell), S303), the UE 3reports the result of the detection to the LTE-U eNB (Proximityindication for unlicensed frequency. S304).

The notification regarding detection of proximity of a cell on theunlicensed frequency may include, for example, at least one of:information about one or more unlicensed frequencies on which theproximity detection is to be performed: and information about cell(s) onthese unlicensed frequency(ies). The information about the unlicensedfrequency(ies) may include, for example, one or any combination of thefollowing items:

-   -   a frequency identifier of LTE (e.g., the EARFCN);    -   an unlicensed frequency identifier (e.g., the Unlicensed        frequency index); and    -   a (center) frequency (e.g., the carrier frequency).

The unlicensed frequency identifier may be defined as a number or anindex newly added to an unlicensed frequency that is available forLTE-U.

The information about the cell(s) on the unlicensed frequency(ies) mayinclude, for example, one or any combination of the following elements:

-   -   a cell identifier (e.g., a PCI, an ECGI, or a Virtual Cell ID);        and    -   an unlicensed frequency cell identifier (e.g., an Unlicensed        Cell ID).

The Virtual Cell ID may be, for example, a scrambling code identifier(e.g., a Scrambling Identity or a Scrambling Code ID) used to transmit areference signal or another signal in the cell on the unlicensedfrequency. The unlicensed frequency cell identifier may be defined as acell number or a cell index newly added to a cell on an unlicensedfrequency.

Furthermore, the aforementioned notification may include another networkidentifier (e.g., a PLMN ID, the TAI, or a TAC). When this notificationincludes these network identifiers, the radio terminal 3 may use thespecified network identifiers to differentiate cell(s) to which theproximity of the radio terminal 3 is to be detected from other cells.

Referring once again to FIG. 8, the explanation will be continued. Basedon the report from the UE 3, the LTE-eNB 1 determines to instruct the UE3 to perform the terminal measurement in the cell (e.g., the Cell 2) onthe unlicensed frequency (e.g., F2) (Decision on UE measurement inunlicensed frequency for UE #1, S305). The LTE-eNB 1 and the UE 3 thenexecute a procedure for the terminal measurement report regarding theunlicensed frequency, similar to the first embodiment (MeasurementConfiguration, Instruction and Reporting for Unlicensed Frequency.S306).

As shown in FIG. 8, in this embodiment, prior to transmitting thecontrol signaling, the radio base station (LTE-U eNB) 1 receives fromthe radio terminal (UE) 3 the result of the detection of proximity ofthe radio terminal (UE) 3 to a non-serving cell(s) on the unlicensedfrequency (e.g., F2) and determines to transmit the control signaling tothe radio terminal (UE) 3 based on the result of the detection of theproximity (or in response to the result of the detection of theproximity). Accordingly, for example, the radio base station (LTE-U eNB)1 can determine prospective UE(s) that can contribute to improvingthroughput by LTE-U based on the result of the detection of proximity tothe cell (e.g., the Cell 2) on the unlicensed frequency (e.g., F2).Therefore, for example, the radio base station (LTE-U eNB) 1 canselectively cause prospective UE(s) 3 that can contribute to improvethroughput by LTE-U to perform the terminal measurement report, which isused for determining whether to allow the radio terminal (UE) 3 toperform LTE-U using the cell on the unlicensed frequency. As a result ofthis, it is expected to reduce the power consumption and also reduce thecontrol information necessary for the terminal measurement report,regarding the UEs 3 that do not have to send the terminal measurementreport. This is especially effective when the operation state of thecell on the unlicensed frequency is dynamically changed, that is, whenOn/Off of the cell is aperiodically switched.

The detection of proximity to a cell on the unlicensed frequency by theradio terminal (UE) includes, for example, detection of a cell-specificsignal transmitted from the radio base station (LTE-U eNB) 1 in thecell. The cell-specific signal contains at least one of a known symboland a known sequence. The cell-specific signal may be, for example, asynchronization signal (in LTE, the synchronization signal includes aPrimary SS (PSS) and a Secondary SS (SSS)), a reference signal (RS), orbasic information (Master Information Block (MIB)) or system information(System Information Block (SIB), e.g., SIB1, S1B2, or SIBx defined forLTE-U) broadcasted in the cell. In this case, the radio terminal 3 maydetect proximity to the cell on the unlicensed frequency based on, forexample, whether the reception quality (e.g., RSRP, RSRQ, RSSI, SINR, orCQI) of the cell-specific signal (e.g., RS) is equal to or larger than apredetermined threshold (or larger than the threshold). Instead, theradio terminal 3 may detect proximity to the cell based on whether ithas successfully received the basic information (MIB) or the systeminformation (SIB) broadcasted in the cell. The reference signal mayinclude, for example, at least one of: a cell specific reference signal(Cell Specific RS (CRS)), a reference signal (CSI RS) for a measurementreport regarding channel state information (CSI), and a reference signalfor cell detection (Discovery RS (DRS)). The DRS may be a combination oftwo or more of the PSS, the SSS, the CRS, and the CSI RS, or may be anew reference signal defined for the cell detection.

When the radio terminal (UE) 3 has received, from the radio base station(LTE-U eNB) 1, the notification regarding the detection of proximity tothe cell on the unlicensed frequency, the radio terminal (UE) 3 mayconsider that it has been configured to perform detection on theunlicensed frequency (i.e., UE considers itself to be configured toperform proximity check for unlicensed frequency), or consider that ithas been configured to transmit a notification (proximity indication)indicating that the proximity to the cell in the unlicensed frequencyhas been detected (i.e., UE considers itself to be configured to provideproximity indication for unlicensed frequency). The “proximity check” isalso referred to as “proximity estimation”. Further, the radio basestation (LTE-U eNB) 1 may explicitly instruct the radio terminal (UE) 3to perform the detection by this notification or may implicitly instructthe radio terminal (UE) 3 to perform the detection by including, in thisnotification, information regarding the unlicensed frequency to bedetected or information regarding the cell on the unlicensed frequency.

Further, the notification regarding the detection of the proximity tothe cell on the unlicensed frequency may be transmitted, for example, asdedicated control information by an RRC signaling (message). In thiscase, the RRC message corresponding to this notification may be an RRCConnection Reconfiguration message and a“ReportProximityUnlicensedConfig” IE may be newly defined as an RRCinformation element (IE) included therein. This IE includes, besidesinformation to enable the function for detecting the proximity to thecell on the unlicensed frequency (i.e., proximityindicationUnlicensed isset to enabled), information about the target unlicensed frequency.Further, the RRC message may contain identification informationregarding the cell on the unlicensed frequency (e.g., a physical cellidentifier (PCI) or a global cell identifier (EUTRAN Cell Global ID(ECGI))). This notification may be transmitted on broadcast information(System Information (SI), System Information Block (SIB)), instead ofthe RRC signaling.

Furthermore, the notification indicating that the proximity to the cellon the unlicensed frequency has been detected (proximity indication) mayalso be transmitted by an RRC signaling (message). In this case, a“ProximityIndicationUnlicensed” message may be newly defined as an RRCmessage corresponding to this notification. This message includes a“ProximityIndicationUnlicensed” IE for indicating the result of thedetection of the proximity to the cell on the unlicensed frequency. ThisIE may include information indicating that the proximity has beendetected and information about the target unlicensed frequency. The IEmay also include identification information about the cell (e.g., PCI orECGI) on the unlicensed frequency that has been detected.

While the detection of proximity to a cell means that the radio terminal3 detects that it has come into the vicinity (area, region) of one ormore cells on the target unlicensed frequency, a case in which the radioterminal 3 has already been in the vicinity of the cell before thedetection of the proximity to the cell is started (attempted) is alsoincluded within the scope of this embodiment. Further, the detection ofthe proximity to a cell may be thought of as being (considered to be) anestimation of the proximity to a cell, detection of availability of acell, or more simply detection (discovery) of a cell.

Third Embodiment

A third embodiment according to the present invention will be described.FIG. 9 is a diagram showing a configuration example of an LTE-U radiocommunication system and another system according to a plurality ofembodiments including this embodiment. The main difference from FIGS. 1Aand 1B is that radio base stations (eNBs) 6 and 7 and a radio terminal(UE) 8 have a Dual Connectivity (DC) function (Non-Patent Literature 5).The Dual Connectivity is processing in which the UE 8 performscommunication simultaneously using radio resources (i.e., cells orcarriers) provided (i.e., managed) by a main base station (master basestation, Master eNB (MeNB)) 6 and a sub base station (secondary basestation, Secondary eNB (SeNB)) 7. In the example shown in FIG. 9, theMeNB 6 and the SeNB 7 are connected to each other via an X2 interface,the MeNB 6 manages Cell #1 on the licensed frequency F1, and the SeNB 7manages both Cell #2 on the licensed frequency F2 and Cell #3 on theunlicensed frequency F3. The MeNB 6 and the SeNB 7 operate as normal LTEeNBs for UEs that do not perform the DC and are able to independentlycommunicate with these UEs in the Cell #1 and the Cell #2, respectively.

The following briefly describes the Dual Connectivity. The UE 8 is ableto perform carrier aggregation (CA) simultaneously using multiple cellsthat are managed by the MeNB 6 and the SeNB 7 and on differentfrequencies. The group of serving cells managed by the MeNB 6 isreferred to as a Master Cell Group (MCG) and the group of serving cellsmanaged by the SeNB 7 is referred to as a Secondary Cell Group (SCG).The MCG includes at least a Primary Cell (PCell) and may further includeone or more Secondary Cells (SCells). The SCG includes at least aPrimary SCell (abbreviated as a pSCell or a PSCell) and may furtherinclude one or more SCells. The pSCell is a cell to which at least thephysical uplink control channel (PUCCH) is allocated and serves as thePCell in the SCG.

The MeNB 6 maintains a connection (S1-MME) with a mobility managementapparatus (Mobility Management Entity (MME)) in a core network (EvolvedPacket Core (EPC)) for the UE 8 executing the DC. Accordingly, the MeNB6 may be referred to as a mobility management point (or a mobilityanchor) for the UE 8. Therefore, control information of the ControlPlane (CP) is transmitted between the MeNB 6 and the UE 8 in the MCG.Control information of the CP regarding the SCG of the SeNB 7 istransmitted between the SeNB 7 and the MeNB 6 (X2 interface) and isfurther transmitted between the MeNB 6 and the UE 8 in the MCG. Forexample, Radio Resource Configuration of the SCG (e.g.,RadioResoureConfigDedicated IE) is transmitted from the SeNB 7 to theMeNB 6 by an inter-node RRC message referred to as “SCG-Configuration”and is transmitted from the MeNB 6 to the UE 8 by an RRC ConnectionReconfiguration message. On the other hand, terminal capabilityinformation (UE-EUTRA capabilities IE) of the UE 8, security information(e.g., S-KeNB) about the SCG, Radio Resource Configuration (e.g.,RadioResourceConfigDedicated IE) of the MCG and the like are transmittedfrom the MeNB 6 to the SeNB 7 by an inter-node RRC message referred toas “SCG-ConfigInfo”.

In the DC, from the viewpoint of the bearer configuration on the UserPlane (UP), three different configurations are supported. The firstconfiguration is an MCG bearer. The MCG bearer is a bearer in whichradio protocols are arranged only in the MeNB 6 in order to use onlyresources (e.g., the MCG) of the MeNB 6 and a connection (S1-U) ismaintained between a gateway apparatus (S-GW or P-GW) and the MeNB 6,similar to normal LTE that does not perform the DC. The secondconfiguration is an SCG bearer. The SCG bearer is a bearer in which theradio protocols are arranged only in the SeNB 7 in order to use onlyresources (e.g., the SCG) of the SeNB 7 and the connection (S1-U) ismaintained between the gateway apparatus (S-GW or P-GW) and the SeNB 7.The third configuration is a Split bearer. The Split bearer is a bearerin which the radio protocols are arranged in both the MeNB 6 and theSeNB 7 in order to use resources (e.g., MCG and SCG) both of the MeNB 6and the SeNB 7. In the Split bearer, the connection (S1-U) is maintainedbetween the gateway apparatus (S-GW or P-GW) and the MeNB 6 and UP data(e.g., PDCP PDU) to be transmitted in the SCG is forwarded, for example,from the MeNB 6 to the SeNB 7 via the X2.

The following describes the details of this embodiment. In the exampleof the DC in FIG. 9, when LAA is achieved by carrier aggregation of theCell #3 on the unlicensed frequency F3 of the SeNB 7 and the Cell #2 onthe licensed frequency F2 of the SeNB 7, the problem may not be solvedonly by the techniques described in the aforementioned first and secondembodiments. This is because the SeNB 7 cannot directly transmit orreceive control information (e.g., RRC, NAS) of the CP to or from theradio terminal (UE 8) when the DC is performed. The configurationinformation for the terminal measurement (MeasConfig) and the reportregarding the result of the terminal measurement (Measurement report)correspond to the control information of the CP. With reference to FIG.10, a control procedure for solving the further problem in the DC willbe described. FIG. 10 is a sequence diagram showing operations of theradio base stations (the MeNB 6 and the SeNB 7) and the radio terminal(UE) 8 according to the third embodiment. The radio terminal (UE) 8 isdenoted as “UE #2” in FIG. 10.

First, the UE 8 establishes a radio connection (RRC Connection) on theCell #1 of the MeNB 6 as the PCell and performs configuration for theDual Connectivity (DC) so as to use the Cell #2 of the SeNB 7 as thepSCell (Dual Connectivity Configuration, S401). Then the MeNB 6 or theSeNB 7 determines whether to require the UE 8 to perform the terminalmeasurement on the unlicensed frequency (e.g., F3) (Decision on UEmeasurement in unlicensed frequency for UE #2, S402). Upon determiningto require the UE 8 of the terminal measurement, the MeNB 6 transmitsthe configuration information (Measurement configuration (MeasConfig))necessary for the terminal measurement on the unlicensed frequency(e.g., F3) to the UE 8 in the Cell #1 using for example an RRCConnection Reconfiguration message (Measurement Configuration forUnlicensed Frequency (e.g., Cell #3 on F3), S403). The Measurementconfiguration may be generated by the SeNB 7 and then be transmitted tothe MeNB 6, or may be generated by the MeNB 6. When the MeNB 6 receivesfrom the UE 8 a completion report of the reception of the configurationinformation (and the reconfiguration in accordance with theconfiguration information), the MeNB 6 may notify the SeNB 7 of thecompletion (Measurement Configuration Complete, S404). The notificationtransmitted in S404 may be included in “SCG-ConfigInfo” of an inter-nodeRRC container. Alternatively, this notification may be transmitted by anSeNB RECONFIGURATION COMPLETE message on the X2 interface (X2AP).

The SeNB 7 then transmits the instruction for the terminal measurementin the cell (e.g., Cell #3 on F3) on the unlicensed frequency by apredetermined control signaling in the Cell #2 (Measurement Instructionfor Unlicensed Frequency (e.g., Cell #3 of F3), S405). The instructionfor the terminal measurement is associated with at least one of: ameasurement timing indicating a timing when the UE 8 should perform theterminal measurement on the unlicensed frequency (e.g., the Cell #3 inF3) (i.e., when the UE 8 shall perform the terminal measurement); and ameasurement period indicating a period in which the UE 8 should performthe measurement (i.e., an appropriate period in which the terminalmeasurement is executed). In other words, the instruction for theterminal measurement (S405) explicitly or implicitly indicates at leastone of the measurement timing and the measurement period (measurableperiod) of the terminal measurement to be performed by the UE 8 on theunlicensed frequency (e.g., the Cell #3 in F3). Since the details of themeasurement timing and the measurement period are the same as thosedescribed in the first embodiment, the descriptions thereof will beomitted. The control signaling in S405 may be transmitted by the MeNB 6.In this case, the SeNB 7 may transmit to the MeNB 6 at least a part ofthe information to be transmitted in the control signaling and the MeNB6 may then transmit this information to the UE 8. Instead, the MeNB 6itself may generate the information to be transmitted in the controlsignaling.

The UE 8 performs the terminal measurement in the Cell #3 in response tothe control signaling (S405), that is, in accordance with theinstruction for the terminal measurement (Measurement, S407) and reportsthe result of the terminal measurement to the MeNB in the Cell #1(Measurement Reporting for Unlicensed Frequency (e.g., Cell #3 on F3),S408). In the terminal measurement (S407), the UE 8 may measure, forexample, reception intensity or reception quality of a reference signal(S406) transmitted from the SeNB 7 in the Cell #3. The terminalmeasurement and the terminal measurement report may be performed notonly in the cell (Cell #3) on the unlicensed frequency (F3) but alsoother cell(s) on F3, in other unlicensed frequency(ies), or in thelicensed frequency. Since the details of the terminal measurement aresimilar to those described in the first embodiment, the descriptionsthereof will be omitted.

The MeNB 6 or the SeNB 7 determines whether to perform communicationwith the UE 8 in the Cell #3 (e.g., downlink data transmission) based onthe result of the terminal measurement that has been reported. When theMeNB 6 or the SeNB 7 determines to perform communication with the UE 8in the Cell #3 managed by the SeNB 7 (Decision on LTE-U for UE #2 inCell #3, S409), the MeNB 6 transmits, to the UE 8 in the Cell #1, radioresource configuration information regarding the Cell #3 (Radio ResourceConfiguration, e.g., RadioResourceConfigCommon,RadioResourceConfigDedicated) (Radio Resource Configuration for Cell #3,S410). In this case, the MeNB 6 may use, for example, an RRC ConnectionReconfiguration message. The radio resource configuration informationregarding the Cell #3 may be generated by the SeNB 7 and then forwardedto the MeNB 6 as SCG-Configuration and the MeNB 6 may transmit the radioresource configuration information to the UE 8. Eventually, the SeNB 7performs LAA with carrier aggregation of the Cell #2 and the Cell #3,and, for example, transmits user data (DL data) to the UE 8 (not shown).

Using the aforementioned procedure, even when the Dual Connectivity isbeing executed, it is possible to appropriately determine the radioterminal 3 that is allowed to perform LTE-U (in the cell) on theunlicensed frequency managed by the SeNB 7. As a result, it can beexpected to improve performance (e.g., system throughput) of the wholeLTE radio communication system.

Specific Example 5

A specific example 5 according to the third embodiment will bedescribed. The specific example 5 provides a procedure for determining,in the MeNB 6 or the SeNB 7, whether to require the UE 8 to perform theterminal measurement on the unlicensed frequency (e.g., F3).

FIG. 11 is a diagram showing an example of operations of the MeNB 6 andthe SeNB 7 including exchange of information (X2 message) in Step S402“Decision on UE measurement in unlicensed frequency for UE #2” shown inFIG. 10. There are two options for the operations of the MeNB 6 and theSeNB 7. In the first option (Option 1), the SeNB 7 determines whether torequire the UE 8 to perform the terminal measurement on the unlicensedfrequency (e.g., F3) (Decision on UE measurement, S501). Upondetermining to require the UE 8 of the terminal measurement, the SeNB 7notifies the MeNB 6 of the information about the target unlicensedfrequency (Available Unlicensed Frequency information, S502). The MeNB 6may respond to this notification (S502) (Available Unlicensed FrequencyInformation Response, S503).

On the other hand, in the second option (Option 2), the SeNB 7 notifiesthe MeNB 6 of the information regarding the target unlicensed frequency(Available Unlicensed Frequency Information, S505) and the MeNB 6 makesthe determination (S506). Then the MeNB 6 transmits the result of thedetermination to the SeNB 7 (Available Unlicensed Frequency InformationResponse, S507). The result of the determination may include informationindicating that the MeNB 6 instructs the UE 8 to perform the terminalmeasurement on the unlicensed frequency, or it may simply include anacknowledgement response (ACK). The aforementioned information regardingthe target unlicensed frequency may be information about the unlicensedfrequency (e.g., EARFCN, Unlicensed frequency index, or carrierfrequency) information about the cell on the unlicensed frequency (e.g.,PCI, the ECGI, Virtual Cell ID, or Unlicensed Cell ID), or a combinationthereof. The information regarding the unlicensed frequency in S502 andS505 may be transmitted by an ENB CONFIGURATION UPDATE message on theX2AP. In particular, this information may be included in a “Served CellsTo Add” IE or a “Served Cells To Modify” IE of this message.

Specific Example 6

A specific example 6 according to the third embodiment will bedescribed. The specific example 6 provides a procedure for determining,in the MeNB 6 or the SeNB 7, whether to allow the UE 8 to perform LTE-Uin the cell on the unlicensed frequency (e.g., Cell #3 on F3).

FIG. 12 is a diagram showing an example of operations of the MeNB 6 andthe SeNB 7 including exchange of information (X2 message) in Step S409“Decision on LTE-U for UE #2 in Cell #3” in FIG. 10. There are twooptions for the operations of the MeNB 6 and the SeNB 7. In the firstoption (Option 1), the MeNB 6 transmits to the SeNB 7 the result of theterminal measurement on the unlicensed frequency received from the UE 8(Measurement results for unlicensed frequency, S601). The SeNB 7determines, based on the result of the terminal measurement, whether toallow the UE 8 to perform LTE-U in the cell on the unlicensed frequency(Cell #3 on F3) (Decision on LTE-U. S602). Upon determining to allow theUE 8 to perform LTE-U, the SeNB 7 generates radio resource configurationinformation (e.g., RadioResourceConfigCommon,RadioResourceConfigDedicated) of the cell (Cell #3) on the targetunlicensed frequency and transmits the generated radio resourceconfiguration information to the MeNB 6 (Radio resource configurationfor Cell #3, S603).

The result of the terminal measurement in S601 may be transmitted in“SCG-ConfigInfo” of an inter-node RRC container. Alternatively, theresult may be transmitted by an SeNB MODIFICATION REQUEST message on theX2AP. Further, the radio resource configuration information in S603 maybe transmitted in “SCG-Configuration” of an inter-node RRC container.Alternatively, the information may be transmitted by an SeNBMODIFICATION REQUEST ACKNOWLEDGE message on the X2AP or may betransmitted by an SeNB MODIFICATION REQUIRED message on the X2AP.

On the other hand, in the second option (Option 2), the MeNB 6determines whether to allow the UE #2 to perform LTE-U in the cell onthe unlicensed frequency (Cell #3 on F3) based on the result of theterminal measurement (Decision on LTE-U, S605). Upon determining toallow the UE 8 to perform LTE-U, the MeNB 6 transmits to the SeNB 7 arequest for adding the cell (Cell #3) on the target unlicensed frequencyto the serving cell(s) (e.g., SCG) (Cell #3 addition request, S606). Theinformation about the Cell #3 included in this request may be indicatedby information about the unlicensed frequency (e.g., EARFCN) and the PCIof the Cell #3, or indicated by the ECGI of the Cell #3, or indicated bya combination thereof. The SeNB 7 generates radio resource configurationinformation (e.g., RadioResourceConfigCommon,RadioResourceConfigDedicated) of the Cell #3 in response to the requestand transmits the generated radio resource configuration information tothe MeNB 6 (Radio resource configuration for Cell #3, S607).

The request in S606 may be transmitted in “SCG-ConfigInfo” of aninter-node RRC container. Alternatively, this request may be transmittedby an SeNB ADDITION REQUEST message on the X2AP or by an SeNBMODIFICATION REQUEST message on the X2AP. Further, the message in S607may be transmitted by “SCG-Configuration”, similar to the messagetransmitted in S603. Further, this message may be transmitted by an SeNBADDITION REQUEST ACKNOWLEDGE message on the X2AP or by an SeNBMODIFICATION REQUEST ACKNOWLEDGE message on the X2AP.

Lastly, configuration examples of the radio base stations (the LTE-U eNB1, the MeNB 6, the SeNB 7) and the radio terminals (the UE 3, the UE 8)according to the aforementioned embodiments will be described. Each ofthe radio base stations (the LTE-U eNB 1, the MeNB 6, the SeNB 7)described in the aforementioned embodiments may include a transceiver tocommunicate with a radio terminal (the UE 3, the UE 8) and a controllerthat is coupled to the transceiver. This controller executes the controlprocedure regarding one of the radio base stations (the LTE-U eNB 1, theMeNB 6, the SeNB 7) described in the aforementioned embodiments (e.g.,control of the terminal measurement on the unlicensed frequencyperformed by a radio terminal (the UE 3, the UE 8)).

Each of the radio terminals (the UE 3, the UE 8) described in theaforementioned embodiments may include a transceiver to communicate witha radio base station (the LTE-U eNB 1, the MeNB 6, the SeNB 7) and acontroller that is coupled to the transceiver. The controller executesthe control procedure regarding one of the radio terminals (the UE 3,the UE 8) described in the aforementioned embodiments (e.g., control ofthe terminal measurement and the reporting regarding the terminalmeasurement).

FIGS. 13 and 14 are block diagrams showing the configuration examples ofthe radio base station 1 and the radio terminal 3 according to the firstembodiment. The radio base stations and the radio terminals according tothe other embodiments may have the configurations similar to those inFIGS. 13 and 14. Referring to FIG. 13, the radio base station 1 includesa transceiver 101 and a controller 102. The transceiver 101 isconfigured to communicate with a plurality of radio terminals includingthe radio terminal 3. The controller 102 is configured to transmit anotification to the radio terminal 3 and to receive the measurementreport from the radio terminal 3 in order to achieve the terminalmeasurement by the radio terminal 3 on the unlicensed frequency.

Referring to FIG. 14, the radio terminal 3 includes a transceiver 301and a controller 302. The transceiver 301 is configured to communicatewith the radio base station 1. The controller 302 is configured tocontrol the terminal measurement on the unlicensed frequency inaccordance with the notification received from the radio base station 1and to transmit the measurement report to the radio base station 1.

Each of the controllers included in the radio base stations and theradio terminals according to the aforementioned embodiments may beimplemented by causing a computer including at least one processor(e.g., a microprocessor, a Micro Processing Unit (MPU), a CentralProcessing Unit (CPU)) to execute a program. Specifically, one or moreprograms including instructions that cause the computer to perform analgorithm regarding the UE or the eNB described with reference tosequence diagrams and the like may be supplied to the computer.

The program(s) can be stored and provided to a computer using any typeof non-transitory computer readable media. Non-transitory computerreadable media include any type of tangible storage media. Examples ofnon-transitory computer readable media include magnetic storage media(such as flexible disks, magnetic tapes, hard disk drives, etc.),optical magnetic storage media (e.g., magneto-optical disks), CompactDisc Read Only Memory (CD-ROM), CD-R, CD-R/W, and semiconductor memories(such as mask ROM, Programmable ROM (PROM), Erasable PROM (EPROM), flashROM. Random Access Memory (RAM), etc.). The program(s) may be providedto a computer using any type of transitory computer readable media.Examples of transitory computer readable media include electric signals,optical signals, and electromagnetic waves. Transitory computer readablemedia can provide the program to a computer via a wired communicationline (e.g., electric wires, and optical fibers) or a wirelesscommunication line.

Other Embodiments

The explanations of the first to third embodiments have been providedwith regard to the case where the unlicensed frequency is used fortransmitting downlink user data. It is needless to say, however, thatthese embodiments can be applied to a case in which the unlicensedfrequency is used for transmitting uplink user data as well. In thiscase, the radio terminal (UE) 3 may perform a process similar to thefirst sensing or the second sensing performed by the radio base station(LTE-U eNB) 1. It is therefore possible to avoid degradation ofperformance of not only the LTE-U system but also other systems, whichis due to transmission of the uplink signal in LTE-U being excessiveinterference to the other systems.

The explanations of the first to third embodiments have been providedwith regard to the case of the LAA. That is, in the first and secondembodiments, carrier aggregation (CA) in which the radio base station(LTE-U eNB) 1 and the radio terminal (UE) 3 use the cell on the licensedfrequency as the primary cell (PCell) and use the cell on the unlicensedfrequency as the secondary cell (SCell) has been mainly described. Inthe third embodiment, the Dual Connectivity (DC) in which the MeNB 6 andthe SeNB 7 use the licensed frequency and the SeNB 7 further uses theunlicensed frequency has been mainly described. However, as alreadystated above, in the first and second embodiments, the radio basestation (LTE-U eNB) 1 may perform carrier aggregation (CA) using ashared frequency (e.g., F3) as the PCell and using an unlicensedfrequency in a narrow sense (e.g., F2) or another shared frequency(e.g., F4) as the secondary cell (SCell). The unlicensed frequency in anarrow sense means a frequency that is not allocated to any operator(i.e., a frequency that is neither the licensed frequency nor the sharedfrequency). In this case, the radio base station (LTE-U eNB) 1 maytransmit, to the radio terminal 3 in the PCell (e.g., F3), the controlsignaling associated with at least one of the measurement timing and themeasurement period of the terminal measurement in the SCell (e.g., F2 orF4). In a similar way, in the third embodiment, the MeNB 6 may use ashared frequency and the SeNB 7 may use a shared frequency or anunlicensed frequency in a narrow sense in the Dual Connectivity (DC).

The explanations of the aforementioned embodiments have been providedwith regard to the LTE system. However, as already stated above, theseembodiments may be applied to radio communication systems other than theLTE system such as the 3GPP UMTS, the 3GPP2 CDMA2000 system (1×RTT,HRPD), the GSM/GPRS system, or the WiMAX system. The radio base station(eNB) and the RRH/RRE having the function of performing the LTEcommunication on the unlicensed frequency have been referred to as aradio base station (LTE-U eNB). In the other systems as well, a networknode capable of communicating on the unlicensed frequency using the samecommunication scheme as that used for the licensed frequency may beintroduced and it may be referred to as a radio station. That is, theradio station corresponds, for example, to a radio base station (eNB)and an RRH/RRE in the LTE as described above, to a base station (NodeB(NB)) and a base station controller (RNC) in the UMTS, or to a basestation (BTS) and a base station controller (BSC) in the CDMA2000system. Further, in the example of the Dual Connectivity (DC) inparticular, a base station system including a main base station (MeNB inLTE) and a sub base station (SeNB in LTE) may be referred to as a radiostation. Each of the main base station and the sub base station may bereferred to as a radio communication node.

Further, in the aforementioned embodiments, the cell on the licensedfrequency in which the control signaling for the instruction for theterminal measurement is transmitted (i.e., the PCell in CA or the celloperated by the MeNB in the DC) and the cell on the unlicensed frequencyto be the target of the terminal measurement (i.e., the SCell in CA orthe cell operated by the SeNB in the DC) may use Radio AccessTechnologies (RATs) different from each other. For example, the cell onthe licensed frequency may be a cell of LTE (E-UTRAN) and the cell onthe unlicensed frequency may be a cell of UMTS (UTRAN).

The embodiments stated above are merely examples regarding applicationsof the technical ideas obtained by the present inventor. These technicalideas are not limited only to the embodiments described above, andvarious modifications may be made as a matter of course.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-186949, filed on Sep. 12, 2014, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   1, 6, 7 RADIO BASE STATION-   3, 8 RADIO TERMINAL-   4 WIRELESS LAN ACCESS POINT-   5 WIRELESS LAN TERMINAL-   101, 301 TRANSCEIVER-   102, 302 CONTROLLER

1-66. (canceled)
 67. A method performed in a radio station thatcomprises a first radio node configured to operate a first cell on afirst licensed frequency and a second radio node configured to operateboth a second cell on a second licensed frequency and a third cell on anunlicensed frequency, the method comprising: communicating with a radioterminal on the first and second licensed frequencies; transmitting, tothe radio terminal from the second radio node in the second cell, ameasurement configuration that includes control information associatedwith a discovery signal measurement to be performed on the unlicensedfrequency, wherein the control information includes: informationindicating periodicity at which a first period, in which the discoverysignal measurement is performed, occurs periodically, and an offsetvalue to indicate a subframe number and a System Frame Number (SFN) atwhich the first period starts; and receiving, from the radio terminal bythe first radio node in the first cell, a result of the discovery signalmeasurement which is performed within the first period which occursperiodically at the periodicity and starts at the subframe number andthe SFN indicated by at least the offset value.